1. Field of the Invention
The present invention relates generally to the production of radioactive stent structures and, more particularly to positioning devices that allow stents to be selectively axially collapsible or reducible to facilitate either mass production or "point-of-use" production of radionuclides by irradiation with intense radiation beams so as to form radioactive stents suitable for therapeutic and/or diagnostic medical purposes.
2. Description of the Related Art
Radioactive materials have been used extensively for many years for therapeutic and/or diagnostic medical purposes. In this regard, radioisotopes are used to kill large volumes of cancer cells directly using large quantities of radioactive material. Alternatively, small amounts of radioisotopes are injected into the body or bloodstream and their position in the body is determined by observing the gamma rays emitted when they decay. Radioisotopes may also be bound to some chemical which is selected for its ability to localize at a problem area in the body thereby aiding in the diagnosis of disease.
Relatively newer therapies propose the use of small amounts of radioactivity to treat small tissue volumes, namely intravascular walls. For example, U.S. Pat. No. 5,059,166 to Fischell et al., the entire content of which is incorporated hereinto by reference, discloses embedding a radioactive isotope material into an existing stent structure, the radioactive material having a half-life of less than 100 days, which stent structure may be embedded into plaque tissue within a patient's arterial wall. The radioactive stent releases radiation so as to decrease the rate of proliferative cell growth of the traumatized arterial wall, i.e., to decrease intimal hyperplasia. As a result of such radiation therapy, restenosis after stent implantation is expected to be significantly reduced.
Another example is the use of esophageal stents to alleviate dysphagia in patients with esophageal cancer. Suppression of tumor regrowth through the stent mesh is a major quality of life concern for these patients. If an easy way of making such stents radioactive can be found, radioactive stents would be utilized.
A further example is the potential use of radioactive stents for the treatment of benign prostatic hyperplasia. Here stents are used to maintain urethral opening. If the stent could simultaneously provide radiation to reduce the affliction causing the stricture this would be advantageous.
Thus, there are many examples where out of control proliferative response (either benign or oncologic) compromises the ability of passageways in the human body to be maintained open. Stents themselves (meaning a rigid mesh structure to provide bracing for the walls) solve the physical-mechanical problem. Radiation from the stent can solve the cellular response that could otherwise grow through the stent and compromise the lumen.
While radiating tissue for medical diagnostic and/or therapeutic purposes is advantageous, there are several real and nontrivial problems associated with such "nuclear medicine", primarily in the availability and/or accessibility of the physician to a source of suitable radioactive devices and materials.